Uncontrolled collision dynamics and the role of dual motor actuators in impact mitigation

• Dual motor actuators reduce collision forces in uncontrolled robot impacts. • Analytical and simulation models predict impact forces with high accuracy. • Experiments confirm lower peak forces compared with single motor actuators. • Collision peaks occur within milliseconds, limiting reaction by control systems. Human-robot interaction involves unavoidable collision risks, especially in uncontrolled impacts where forces rise rapidly. Conventional single-drive actuators (SDAs) exhibit high reflected inertia, limiting their intrinsic safety and motivating actuator designs that can passively reduce impact severity. This paper investigates Dual Motor Actuators (DMAs) as a promising solution for passive impact mitigation. We develop a high-fidelity collision model and a complementary analytical formulation that together capture the dynamics of robot-human collisions, including the influence of actuator inertia distribution. The models are validated through simulations and experiments using high-frequency force measurements at 2 kHz. Experimental and simulation results show that DMAs can passively reduce peak impact forces by up to 34% compared to SDAs, despite identical output torque capability. The analytical model accurately predicts peak forces and time-to-peak across a wide range of conditions, showing that collisions reach their maximum force within 17–79 ms. This narrow response window aligns with the experimentally observed 9 ms detection latency at a 1 kHz sampling rate, underscoring the importance of intrinsic mechanical safety. Together, these results demonstrate that DMAs offer a robust actuator architecture for passive impact mitigation and provide actionable design insights for safer collaborative and humanoid robots.